Temperature-Sensitive Paint Method for the Investigation of Stationary Crossflow Instability Induced Boundary Layer Transition

Abstract

Laminar-turbulent boundary-layer transition in the Swept flat PlatE Crossflow TRAnsition (SPECTRA) configuration is investigated by means of the Temperature-Sensitive Paint method and Hot-Wire Anemometry. The results of both measurement techniques are compared in detail far upstream of the transition and also in the transition region in order to investigate the capabilities of TemperatureSensitive Paint to obtain the wavelength of stationary crossflow (CF) instabilities in the laminar flow, to ascertain the detectability of the transition onset and to determine the transition location. The Temperature-Sensitive Paint method captures the footprints of stationary crossflow vortices and resolves the dominant crossflow wavelength already at low amplitudes of the crossflow disturbance. The chordwise transition location, as detected by the Temperature-Sensitive Paint method, agrees with the maximum in the chordwise evolution of the root-mean square of the high-pass filtered velocity fluctuations. Furthermore, the detected chordwise location of the onset of the secondary instabilities from Hot-Wire Anemometry measurements coincides with the local surface temperature gradient observed by the Temperature-Sensitive Paint method. Finally, the Temperature-Sensitive Paint method was used to investigate the influence of a backward-facing step of .0.45 mm height on the Transition location.